Method and system for compensating thermally induced motion of probe cards

ABSTRACT

The present invention discloses a method and system compensating for thermally induced motion of probe cards used in testing die on a wafer. A probe card incorporating temperature control devices to maintain a uniform temperature throughout the thickness of the probe card is disclosed. A probe card incorporating bi-material stiffening elements which respond to changes in temperature in such a way as to counteract thermally induced motion of the probe card is disclosed including rolling elements, slots and lubrication. Various means for allowing radial expansion of a probe card to prevent thermally induced motion of the probe card are also disclosed. A method for detecting thermally induced movement of the probe card and moving the wafer to compensate is also disclosed.

This application is a continuation in part of application Ser. No.10/003,012 filed Nov. 2, 2001 entitled METHOD AND SYSTEM FORCOMPENSATING THERMALLY INDUCED MOTION OF PROBE CARDS.

BACKGROUND OF THE INVENTION

The present invention relates to probe cards having electrical contactsfor testing integrated circuits, and more specifically for a system andmethod to compensate for thermally induced motion of such probe cards.Probe cards are used in testing a die, e.g. integrated circuit devices,typically on wafer boards. Such probe cards are used in connection witha device known as a tester (which as discussed herein also refers to theprober) wherein the probe card is electronically connected to the testerdevice, and in turn the probe card is also in electronic contact withthe integrated circuit to be tested.

Typically the wafer to be tested is loaded into the tester securing itto a movable chuck. During the testing process, the chuck moves thewafer into electrical contract with the probe card. This contact occursbetween a plurality of electrical contacts on the probe card, typicallyin the form of spring contacts, and plurality of discrete connectionpads (bond pads) on the dies. Several different types of electricalcontacts are known and used on probe cards, including without limitationneedle contacts, cobra-style contacts, spring contacts, and the like. Inthis manner, the semiconductor dies can be tested and exercised, priorto singulating the dies from the wafer.

For effective contact between the electrical contacts of the probe cardand the bond pads of the dies, the distance between the probe card andthe wafer should be carefully maintained. Typical spring contacts suchas those disclosed in U.S. Pat. Nos. 6,184,053 B1, 5,974,662 and5,917,707, incorporated herein by reference, are approximately 0.040″,or about one millimeter, in height. If the wafer is too far from theprobe card contact between the electrical contacts and the bond padswill be intermittent if at all.

While the desired distance between the probe card and wafer may be moreeasily achieved at the beginning of the testing procedure, the actualdistance may change as the testing procedure proceeds, especially wherethe wafer temperature differs from the ambient temperature inside thetester. In many instances, the wafer being tested may be heated orcooled during the testing process. Insulating material such as platinumreflectors may be used to isolate the effects of the heating or coolingprocess to some extent, but it cannot eliminate them entirely. When awafer of a temperature greater than that of the probe card is movedunder the card, the card face nearest the wafer begins to changetemperature. Probe cards are typically built of layers of differentmaterials and are usually poor heat conductors in a direction normal tothe face of the card. As a result of this a thermal gradient across thethickness of the probe card can appear rapidly. The probe card deflectsfrom uneven heat expansion. As a result of this uneven expansion, theprobe card begins to sag, decreasing the distance between the probe cardand the wafer. The opposite phenomenon occurs when a wafer is coolerthan the ambient temperature of the tester is placed near the probecard. As the face of the probe card nearest the wafer cools andcontracts faster than the face farthest from the wafer, the probe cardbegins to bow away from the wafer disrupting electrical contact betweenthe wafer and the probe card.

SUMMARY OF THE INVENTION

The invention is set forth in the claims below, and the following is notin any way to limit, define or otherwise establish the scope of legalprotection. In general terms, the present invention relates to a methodand system from compensating for thermally or otherwise induced motionof probe cards during testing of integrated circuits. This may includeoptional features such as energy transmissive devices, bi-materialdeflecting elements, and/or radial expansion elements.

One object of the present invention is to provide an improved method andsystem for compensating thermally induced motion of probe cards.

Further objects, embodiments, forms, benefits, aspects, features andadvantages of the present invention may be obtained from the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a probe card.

FIG. 2 is a cross-sectional view of a probe card engaged with a wafer.

FIG. 2A is a cross-sectional view of a thermally distorted probe cardengaged with a wafer.

FIG. 2B is a cross-sectional view of a thermally distorted probe cardengaged with a wafer.

FIG. 3 is a cross-sectional view of a probe card assembly.

FIG. 4 is an exploded, cross-sectional view of a probe card according toone example of the present invention.

FIG. 4A is a cross-sectional view of the probe card of FIG. 4.

FIG. 4B is a top plan view of another example of a probe card accordingto the present invention.

FIG. 5 is an exploded, cross-sectional view of a probe card according toanother example of the present invention.

FIG. 5A is a cross-sectional view of the probe card of FIG. 5.

FIG. 6 is an exploded, cross-sectional view of a probe card according toanother example of the present invention.

FIG. 6A is a cross-sectional view of the probe card of FIG. 6.

FIG. 6B is a bottom plan view of the probe card of FIG. 6.

FIG. 7 is an exploded, cross-sectional view of a probe card according toanother example of the present invention.

FIG. 7A is a cross-sectional view of the probe card of FIG. 7.

FIG. 8 is a cross-sectional view of a probe card according to yetanother example of the present invention.

FIG. 9 is an exploded, cross-sectional view of a probe card according toanother example of the present invention.

FIG. 9A is a cross-sectional view of the probe card of FIG. 9.

FIG. 10 is a flowchart depicting one example of a control programaccording to the present invention.

FIG. 11 is a front diagrammatic view of a prober and a tester connectedby two communication cables according to one embodiment of the presentinvention.

FIG. 12 is a side diagrammatic view of the prober of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, and alterations and modifications in theillustrated device and method and further applications of the principlesof the invention as illustrated therein, are herein contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

FIG. 1 shows a typical example of a probe card 110 and wafer 140 loadedinto a tester. In this and the other accompanying views certain elementsof certain components are shown exaggerated, for illustrative clarity.Additional components which may be mounted to the probe card, such asactive and passive electronic components, connectors, and the like, areomitted for clarity. The present invention may be practiced withvariations of the basic probe card design examples shown, such as probecards incorporating interposers as shown in U.S. Pat. No. 5,974,662,which is hereby incorporated by reference. No limitation of the scope ofthe invention is intended by the omission of these elements.

The probe card 110 is supported by the head plate 120 when mounted inthe tester parallel to the die on a wafer 140, and most typicallypositioned directly above it. The probe card 110 is typically round,having a diameter on the order of 12 inches, although other sizes andshapes are also contemplated. The probe card 110 is generally aconventional circuit board substrate having a plurality (two of manyshown) of electrical contacts 130 disposed on the wafer side 114thereof. The electrical contacts are known in the industry andhereinafter referred to as “probes” or “probe elements”. A preferredtype of probe element is spring contacts, examples of which aredisclosed in U.S. Pat. Nos. 6,184,053 B1; 5,974,662; and 5,917,707 whichare hereby incorporated by reference. However, many other contacts areknown in the industry (e.g., needle contacts and cobra-style contacts)and any such contact may be included in any embodiment of the probecards of the present invention. Typically, the probe card is connectedto the testing machine by other electrical contacts (not shown).

As is known, a semiconductor wafer 140 includes a plurality of die sites(not shown) formed by photolithography, deposition, diffusion, and thelike, on its front (upper, as viewed) surface. Each die site typicallyhas a plurality (two of many shown) of bond pads 145, which may bedisposed at any location and in any pattern on the surface of the diesite. Semiconductor wafers typically have a diameter of at least 6inches, but the use of the present invention to test wafers of othersizes and shapes is also contemplated.

Once the wafer 140 is mounted in the testing device, wafer chuck 150including table actuator 155 lift the integrated wafer 140 vertically inthe Z-axis direction (see FIG. 2) to allow electronic contact betweenprobes 130 and a corresponding pad (such as pads 145) of the wafer 140.The lifting mechanism may utilize a scissors mechanism, telescopingaction, lever action, thread action, cam action or other liftingmechanisms. Such lifting mechanism, as with the other movements in theother embodiments, may be actuated by a variety of mechanisms such aspneumatics, stepper motors, servo motors or other electrical motors orotherwise and are typically robotically controlled. Such liftingmechanism may also allow for movement in the X and Y directions, tilt,and rotation. Once the wafer 140 is moved into electrical contact withthe probe card 110 (as shown in FIG. 2), the testing procedure mayproceed.

FIG. 2 illustrates a wafer 140 in electrical contact with a probe card110. The pressure contact of the probe elements 130 with the bond pads145 provide this contact. For this contact to be produced, the wafer 140is urged to an effective distance Z (vertical as shown) from the probecard. Typically, the height of the probes 130 used in the probe card isapproximately 0.040″, or about one millimeter, although probe cardcontacts of other heights are also contemplated by the presentinvention. As the probes 130 are generally somewhat flexible, theeffective distance Z between the probe card 110 and the wafer 140 maydiffer from the height of the probes 130 being used. Of course thepresent invention naturally may be modified in accordance with theparticular height or type of a particular probe card's electricalcontacts.

FIGS. 2A and 2B illustrate the thermally induced motion of probe cardsthe present invention is directed towards. As shown in FIG. 2A, a wafer140 having a temperature greater than the ambient temperature of thetester is engaged with the probe card 110. The card face nearest thewafer 114 begins to change temperature. As probe card assemblies aretypically poor conductors of heat in a direction normal to the face ofthe card, a thermal gradient rapidly develops across the thickness ofthe probe card. The probe card behaves as a bimetallic element as theface nearest the wafer 114 warms and therefore expands more quickly thanthe face farthest from the wafer 112. As a result of this unevenexpansion the probe card begins to sag. This movement decreases theactual distance Z′ between the probe card 110 and the wafer 140 tosomething less than the optimal effective distance. Decreasing thedistance between the probe card 110 and the wafer 140 may result inmovement of the probes 130 leading to overengagement of the probes 130from the bond pads 145 and possibly deformation or even breaking theprobe elements 130 or the semiconductor device being tested.

The opposite phenomenon occurs when a wafer 140 significantly coolerthan the ambient temperature of the tester is placed near the probe card130. As the face of the probe card nearest the wafer 114 cools it beginsto contract faster than the face farthest from the wafer 112. As aresult of this uneven cooling, the probe card 110 begins to bow awayfrom the wafer creating an actual distance Z′ between the wafer 140 andthe probe card 110 greater than the optimal effective distance. If greatenough this bow may disrupt electrical contact between the wafer 140 andthe probe card 110 by disengaging some of the probes 130 from theircorresponding bond pads 145.

As seen in FIG. 3, one solution to the problem of thermally induced orother motion of probe cards known in the art is the addition ofstiffening elements 360, 365 to the probe card 110. Typically circularand made of metal, both wafer side stiffeners 360 and tester sidestiffeners 365 are commonly employed. These stiffeners may be affixed inany suitable manner, such as with screws (not shown) extending throughcorresponding holes (not shown) through the probe card 110, therebycapturing the probe card 110 securely between the wafer side stiffener360 and tester side stiffener 365. The stiffeners may also beindividually mounted directly to the probe card 110 such as with screws(not shown). The use of stiffeners, however, may also lead to thermallyinduced movement of the probe card. As the metal stiffeners conduct heatbetter than the probe card 110, a thermal gradient can appear causingthe metal stiffener on one side of the probe card 110 to expand morethan the metal stiffener on the other side of the probe card 110.

FIG. 4 shows an exploded, cross-sectional view of one example of thepresent invention. Although certain elements have been exaggerated forclarity, the dashed lines in the figure properly indicate the alignmentof the various components. This example is a probe card assemblyincorporating at least one energy transmissive device 470, 475 tocompensate for thermally induced motion of the probe card. At least onesuch energy transmissive element 470, 475 is disposed between the probecard 110 and the stiffening elements 360, 365. In an another example ofthe present invention, two such energy transmissive devices 470, 475 areutilized, preferably one adjacent to the tester side of the probe card112 and one adjacent to the wafer side of the probe card 114. Theseenergy transmissive devices 470, 475 may be embedded in the stiffeners360, 365 as shown, but this is not necessary. In yet another example ofthe present invention, a plurality of energy transmissive elements 470A,470B, 470C (FIG. 4B) are disposed between the probe card 110 and thestiffening elements 360, 365. Preferably this plurality of energytransmissive elements is arranged in a generally circular pattern. Also,the individual elements of the plurality of energy transmissive devicesmay be operably linked so they may be controlled together. The presentinvention also contemplates the use of a plurality of energytransmissive elements where the individual elements are generallytriangular and arranged generally forming a circle. The individualelements may also be generally ring shaped and arranged generally asconcentric rings as seen in FIG. 4B. The present invention alsocontemplates a combination of generally triangular and ring shapedindividual energy transmissive elements. Of course, other shapes mayalso be used, including without limitation rectangular (e.g., fourrectangular heaters).

Any suitable energy transmissive device may be utilized to practice thisparticular example of the present invention. For example, thermalelements such as thin film resistance control devices are particularlysuited to the present invention. Thermal elements which allow for bothheating and cooling such as devices which absorb or give off heat at theelectrical junction of two different metals (i.e. a Peltier device) mayalso be used. Energy transmissive devices which do not rely on thermalenergy are also contemplated by the present invention. Devices whichgenerate a mechanical force when a voltage is applied (i.e. apiezoelectric device) may also be used.

Energy transmissive devices 470, 475 which are thermal control elementsmay be utilized to compensate for thermally induced motion of the probecard 110 in several ways. For example, the temperature control devicesmay be operated continually at the ambient temperature of the tester orat some other preselected temperature. This would tend to drive theprobe card 110 to a uniform temperature regardless of the temperature ofthe wafer 140 and thereby prevent deformation of the probe card 110.Alternatively, the temperature control elements 470, 475 may incorporatea temperature sensing element 490, 495. By sensing the temperature ofthe two sides 112, 114 of the probe card, the temperature controlelements 470, 475 may be directed to apply or remove heat as required tocompensate for any thermal gradient developing within the probe card110. It is understood that the control methods described hereinabovewhile making reference to an example of the present inventionincorporating two temperature control elements 470, 475 are equallyapplicable to alternate examples employing a single temperature controldevice or a plurality of control devices.

Energy transmissive devices 470, 475 according to the present inventionmay also be operated by monitoring conditions of the probe card 110other than temperature. For example, a device such as a camera, laser,or other suitable means may be used to monitor the actual distance Z′(see FIG. 2A) between the probe card 110 and the wafer 140. When thisdistance differs from the optimal distance Z by a preselected amount,the energy transmissive devices 470, 475 are engaged to correct thisdeviation. A logic loop control as described in the discussion of FIG.10 may also be used. The present invention also contemplates the use ofenergy transmissive devices 470, 475 similar to those shown to controlthe temperature of elements which hold or support the probe card 110such as head plate 120 as seen in FIG. 1. Alternatively, the probe card110 and mechanical elements in thermal contact with the probe card 110may be brought to temperature equilibrium prior to start of testing.This may be accomplished, for example, using a temperature controlledchamber.

Referring to FIG. 5, this drawing shows an alternate example of thepresent invention utilizing a bi-material stiffening element 580 tocompensate for thermally induced motion of the probe card 110. Althoughcertain elements have been exaggerated for clarity, the dashed lines inthe figure properly indicate the alignment of the various components.The materials used in the bi-material stiffening element preferablyexpand at different rates to the input of energy. For example, the uppermaterial 582 may have a different coefficient of thermal expansion thanthe lower material 584 such that the two materials will react totemperature changes at different rates. Typically the layers of thebi-material stiffening element will be composed of two metals havingdifferent coefficients of thermal expansion although other materialssuch as ceramics and plastics may also be used. The materials,distribution (or location), and/or thickness (or some combinationthereof) of the materials are chosen such that the bow created in thebi-material stiffening element 580 counteracts the expected bow of theprobe card 110 for a particular application. For example, if the wafer140 (which is typically located below the probe card 110 as shown inFIG. 2) is to be heated to a temperature greater than the ambienttemperature of the tester, the bi-material stiffening element 580 wouldbe selected such that the upper material 582 would have a greatercoefficient of thermal expansion than the lower material 584. This wouldcause the upper material 582 to expand more rapidly than the lowermaterial 584 giving the bi-material stiffening element 580 an upward bowto counteract the expected bow of the probe card 110 (as shown in FIG.2A). Although not shown in FIG. 5, the present invention alsocontemplates the use of bi-material stiffening elements in place of thetester side stiffening element 365 as well as the use of multiplebi-material stiffening elements in the place of a single bi-materialstiffening element. Additionally, the bi-material stiffening elements ofthe present invention may be attached to the probe card 110 by meansdescribed hereinabove for the attachment of stiffening elements to probecards or by any other suitable method. The present invention alsocontemplates the use of a bi-material stiffener such that the probe card110 is disposed between the layers of the bi-material stiffener.Alternatively, the probe card 110 may be made of one of the materialssuch that the probe card itself constitutes one of the materials of thebi-material stiffener.

FIGS. 6 and 7 illustrate variations of another example according to thepresent invention. The dashed lines in the figures properly indicate thealignment of the various components although certain elements have beenexaggerated for clarity. This particular example of the presentinvention incorporates a means for allowing radial movement of the probecard 110 relative to the wafer side stiffening element 360. This radialmovement means is disposed between the probe card 110 and the wafer sidestiffening element 360. Specifically shown are rolling members 690 (FIG.6) and lubricating layer 792 (FIG. 7), although other means for allowingradial motion of the probe card 110 relative to the wafer side stiffener360 are also contemplated. The rollers 690 may be ball bearings,cylindrical bearings, or any other suitable shape. The lubricating layer792 may be a layer of graphite or other suitable material.Alternatively, the lubricating layer 792 may be a low-friction filmcomposed of a material such as diamond or Teflon®, or any other suitablematerial. This lubricating layer may be applied to the surface of theprobe card 110, the surface of the stiffening element 360, 365, or both.

Although a fastening means between the probe card 110 and the wafer sidestiffening element 360 is omitted from the illustration, it isunderstood that any suitable fastening method may be used. The waferside stiffening element 360 may be fastened to the tester sidestiffening element 365 or alternatively directly to the probe card 110as described hereinabove. Although known fastening methods such as boltsor screws will typically allow for sufficient radial movement betweenthe probe card 110 and the wafer side stiffening element 360, thepresent invention also contemplates the use of a fastening meansallowing for greater radial movement such as radially oriented slots,dovetails or tracks. As shown in FIG. 6B, the wafer side stiffeningelement 360 may be fastened to the probe card 110 by bolts 692 whichpass through slots 694 in the wafer side stiffening element 360. Thesebolts 692 may be fastened directly to the probe card 110 or mayalternatively pass through holes (not shown) in the probe card 110 andfasten to the tester side stiffening element (not shown).

The example of the present invention illustrated in FIGS. 6 and 7compensates for thermally induced motion of a probe card in thefollowing manner. In the case of a probe card 110 exposed to a wafer 140at a higher temperature than the ambient temperature of the tester, atemperature gradient begins to develop across the probe card 110. Thewafer side of the probe card 114 begins to expand more rapidly than thetester side 112 of the probe card. As the wafer side of the probe card114 begins to expand, the rollers 690 allow for radial motion of theprobe card 110 relative to the wafer side stiffening element 360.Typically only a small amount of radial motion is necessary to preventdeformation of the probe card. In some cases, movement of 10 to 20microns is sufficient, although the present invention also contemplatesembodiments allowing for greater and lesser degrees of radial motion.

Yet another example of the present invention may be described byreferring to FIG. 8. In this particular example of the presentinvention, the distance between the wafer 140 and the probe card 110 iscorrected during the testing procedure to compensate for thermallyinduced motion of the probe card. As previously described, once thewafer 140 is secured in the tester to the wafer chuck 150 it is moved tothe effective distance Z from the probe card 110 to allow for engagementof the probes 130 with the bond pads 145. As testing proceeds, a thermalgradient in the probe card 110 may be induced by proximity to a wafer140 at a temperature significantly different from that of the testerleading to thermally induced motion of the probe card 110 as shown inFIGS. 2A and 2B. To compensate for this motion, the present inventionalso contemplates a system whereby the distance Z between the probe card110 and the wafer 140 is monitored during the testing procedure. Asthermally induced motion begins the actual distance between the probecard 110 and the wafer 140 may change, this alteration is detected andthe wafer 140 is returned to the optimally effective distance Z. Forexample, if the probe card began to sag as shown in FIG. 2A, thedecrease in the actual distance Z′ between the probe card 110 and thewafer 140 is detected and the table actuator 155 lowered to return thewafer 140 to the optimal effective distance Z from the probe card.

The actual distance between the probe card 110 and the wafer 140 may bemonitored by any suitable means. Once such means includes monitoring thepressure exerted on the probe elements 130 by the bond pads 145. Changesin this pressure can be monitored and a signal relayed to the controlsystem for the table actuator to order a corresponding correctivemovement of the wafer 140. This is but one specific example of a meansfor monitoring the distance between the wafer 140 and the probe card110. Other means for monitoring this distance such as the use of lasers,including proximity sensors, captive proximity sensors, or cameras 500are also contemplated by the present invention. Such sensors may be apart of the tester or alternatively may be incorporated in the probecard.

Preferably the actual distance Z′ between the wafer 140 and the probecard 110 is monitored by a computer using a logic loop similar to thatshown in FIG. 10. After the user inputs the desired distance Z betweenthe wafer 140 and the probe card 110 to be maintained 10, indicates themaximum allowable deviation from this distance 20, and any otherinformation specific to the particular testing procedure, the testingprocedure begins. The computer begins by detecting the actual distanceZ′ between the wafer 140 and the probe card 110 at the step labeled 30using a suitable detecting means as previously described. The computerthen compares the actual distance Z′ to the desired distance Z at thestep labeled 40. If the absolute magnitude of the difference between Zand Z′ is greater than the maximum allowable deviation as set at box 20,then the computer applies the appropriate corrective action 80 beforereturning to box 30 to begin the loop again. If the absolute magnitudeof the difference between Z and Z′ is less than the maximum allowabledeviation as set at box 20, then the computer returns to the beginningof the logic loop 30. The corrective action taken at box 80 will ofcourse depend on which particular corrective device or combination ofdevices as previously described are used with a particular probe card.Preferably where more than one device according to the present inventionis used in a single probe card, a single computer will control all suchdevices, although this is not necessary. Preferably the control computeris a part of the tester although alternatively it may be incorporated onthe probe card.

Control of the actual distance between the probe card 110 and the wafer140 as previously described also compensates for probe card deformationother than thermally induced deformation. As the probe elements 130 aregenerally located near the center of the probe card 110 as seen in FIG.1, the engagement of the probe elements 130 with the bond pads 145imparts an upward (as shown) force on the center of the probe card 110.This force may lead to a deformation of the probe card 110 characterizedby a bow near the center of the card. The control system previouslydescribed may also correct for this type of probe card deformation bymonitoring and correcting the actual distance between the probe card 110and the wafer 140.

FIGS. 11 and 12 show diagrammatic views of one example of a prober and atester usable in connection with the present invention. In thisparticular embodiment, prober 100 is physically separate from tester180. They are connected by one or more cables, such as communicationcable 180 a and 180 b as illustrated. Cable 180 a connects to the testhead of the prober which is connected to probe card 110 by electricalconnections 110 a. Probe card as probes 130 as previously described. Inthis embodiment, wafers, such as wafer 140 on stage 150, may be placedfrom the wafer boat 170 by robotic arm 160. Tester 180 generates testdata which is sent to the tester 190 via communications cable 180 a andmay receive response data from the tester via communications cable 180a. The test head 190 receives data from the test head 180 and passes thetest data through the probe card 110 to the wafer. Data from the waferis received through the probe card and sent to the tester. The proberhouses, in the preferred embodiment, the wafer boat stager robotic armas illustrated. The tester may control the prober in a variety of ways,including communication cable 180 b. The wafer boat 170 stores wafers tobe tested or that have been tested. The stage supports the wafer beingtested, typically moving it vertically and horizontally. Typically, thestage is also capable of being tilted and rotated and is capable ofmoving the wafer being tested against probes 130. This may comprise awafer chuck and table actuator as previously described. The robotic arm160 moves wafers between stage 150 and the wafer boat 170.

The tester is typically a computer, and the prober typically alsoincludes a computer or at least a computer-like control circuitry (e.g.a microprocessor or microcontroller and microcontroller or microcode).Test head 190 may similarly include computer or computer-like controlcircuitry. In the preferred embodiment the computer which carries outthe acts illustrated in FIG. 10 is preferably located in the prober.This may be an existing computer, or computer-like control circuitryalready in the prober or alternatively a new computer added to theprober for this purpose. Alternatively, the computer may be located inthe tester 180, in which case feedback signals regarding the position ofthe wafer with respect to the probe card would be typically communicatedto the tester via communication cable 180 b. The control signalsremoving the stage are likewise communicated via that cable.

As yet another alternative, the computer may be located in the test head190 the suitable communication means between the prober 100 and testhead 190. Such communication means may be via wired connections, RFtransmissions, light or other energy beam transmissions and the like.

Yet another alternative, a separate computer distinct from the tester,test head and prober, could be used and connected electrically to theprober for this purpose.

As yet another alternative, a computer, microprocessor, microcontrollerand the like may actually be made part of the probe card 110 for theappropriate input and output connections to facilitate the running ofsteps of FIG. 10. For example, in this way each probe card may have as apart of or imbedded therein its own dedicated and/or customizedalgorithm acts and/or parameters such as those provided for inconnection with FIG. 10.

Probe cards need not be limited to a single device described herein tocompensate for thermally induced motion according to the presentinvention. Indeed, the present invention contemplates the combinationtwo or more of the devices previously described in a single probe card.The example shown in FIG. 9 employs a tester side energy transmissivedevice 470, a wafer side energy transmissive device 475, a lubricatinglayer 792 to allow for radial motion of the probe card 110, and abi-material stiffening element 580. Other combinations using two or moreof the previously described devices to compensate for thermally inducedmotion in probe cards are also contemplated. Preferably any probe cardincorporating two or more of the above-described devices would alsoinclude a control means capable of controlling all of the devicesincorporated, but the present invention also contemplates utilizingindividual control means or no control means in any particular probecard.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment have been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected. The articles “a”, “an”, “said” and “the”are not limited to a singular element, and include one or more suchelement.

1. A method for adjusting a probe card, comprising: placing a probe cardin a prober; measuring a first distance from a known position to aposition of said probe card; comparing via microprocessor means saidfirst distance to a second distance to determine a variancetherebetween; and, when said microprocessor determines said varianceexceeds a determined value, electrically signally means for transmittingenergy to said probe card to selectively deflect said probe card tocontrol the geometric planarity of said probe card.
 2. The method ofclaim 1 wherein said comparing and signaling are done repetitively untilsaid variance does not exceed said determined value.
 3. The method ofclaim 2 wherein said measuring is with an optical sensor.
 4. The methodof claim 3 wherein said microprocessor is in a test head on said prober.5. The method of claim 3 wherein said microprocessor is in a tester thatis physically separate from said prober and is connected thereto bymeans for data communication.
 6. The method of claim 3 wherein saidmeans for transmitting energy transmits thermal energy to said probecard.
 7. The method of claim 3, wherein said probe card comprises abi-metallic element connected thereto to impart deflection.
 8. Themethod of claim 1 wherein said measuring is with an optical sensor. 9.The method of claim 1 wherein said microprocessor is in a test head onsaid prober.
 10. The method of claim 1 wherein said microprocessor is ina tester that is physically separate from said prober and is connectedthereto by means for data communication.
 11. The method of claim 1wherein said means for transmitting energy transmits thermal energy tosaid probe card.
 12. The method of claim 1, wherein said probe cardcomprises a bi-metallic element connected thereto to impart deflection.13. A system for adjusting geometric planarity of a probe card,comprising: a prober for receiving a probe card; means for measuring adistance indicating a position of said probe card; computer means forcomparing said first distance to a second distance to determine avariance therebetween; and means for electrically signaling in responseto said variance exceeding a value, said means for signally transmittinga signal to activate means for transmitting energy to said probe card toselectively deflect said probe card to control the geometric planarityof said probe card.
 14. The system of claim 13, wherein said means fortransmitting energy comprises an energy transmissive element which is athermal element employing thermal energy to selectively deflect aportion of said probe card.
 15. The system of claim 13 and furtherincluding a temperature sensor for monitoring temperature correspondingto deflection of said probe card.
 16. The system of claim 13 and furtherincluding a stiffening element attached to a face of said probe card andadapted to provide structural resistance to planarity deflection of saidprobe card.
 17. The system of claim 13 and further comprising means forfacilitating radial expansion/contraction of said probe card withrespect to a stiffening element.
 18. The system of claim 13 and furtherincluding a multi-layer element having a first layer and a second layer,said first layer and said second layer having different rates ofexpansion per unit of energy, said multi-layer element being attached tosaid probe card, wherein exposing said multi-layer element to energycauses said multi-layer element to selectively impart deflective forcesto a portion of said probe card.
 19. A method of using a probe card,said method comprising: bringing a probe card to within an initialdistance of an electronic device to be tested; monitoring an actualdistance of said probe card from said electronic device; and adjustingsaid actual distance if said actual distance becomes smaller or greaterthan a predetermined range of allowable distances, wherein said methodfurther comprises testing said electronic device, and said monitoringstep and said adjusting step are performed at least in part during saidtesting step.
 20. The method of claim 19, wherein: said probe card ispart of an apparatus having a plurality of probes, and said bringingstep comprises bringing ones of said probes into contact with saidelectronic device to be tested.
 21. The method of claim 20, wherein saidmonitoring step comprises monitoring a pressure of said probes againstsaid electronic device.
 22. The method of claim 20, wherein: saidbringing step comprises moving said electronic device into contact withsaid ones of said probes, and said adjusting step comprises moving saidelectronic device.
 23. The method of claim 19, wherein: said bringingstep comprises moving said electronic device, and said adjusting stepcomprises moving said electronic device.
 24. A method of using a probecard, said method comprising: bringing a probe card to within an initialdistance of an electronic device to be tested; monitoring an actualdistance of said probe card from said electronic device; and adjustingsaid actual distance if said actual distance becomes smaller or greaterthan a predetermined range of allowable distances, wherein saidadjusting step comprises controlling an energy transmissive devicedisposed adjacent said probe card.
 25. The method of claim 24, whereinsaid energy transmissive device comprises a thermal element.
 26. Themethod of claim 25, wherein said thermal element is capable of heatingat least a portion of said probe card.
 27. A method of using a probecard, said method comprising: bringing a probe card to within an initialdistance of an electronic device to be tested; monitoring an actualdistance of said probe card from said electronic device; and adjustingsaid actual distance if said actual distance becomes smaller or greaterthan a predetermined range of allowable distances, wherein saidadjusting step comprises heating a portion of said probe card.
 28. Amethod of using a probe card, said method comprising: bringing a probecard to within an initial distance of an electronic device to be tested;monitoring an actual distance of said probe card from said electronicdevice; and adjusting said actual distance if said actual distancebecomes smaller or greater than a predetermined range of allowabledistances, wherein said adjusting step comprises: determining whether toheat or cool a portion of said probe card, and heating or cooling saidportion of said probe card in accordance with said determining step.